PENTAGON - Eighteen years after the deadliest terror attack on U.S. soil, the world's military spending is at an all-time high.

According to data from the Stockholm International Peace Research Institute, military spending was $1.8 trillion in 2018 alone, which SIPRI Senior Researcher Pieter Wezeman called a "worrying trend."

"We have to see that as a warning signal, not necessarily something which will lead to war, but something which needs very close attention," Wezeman told VOA.

Military spending hit a post-Cold War low in 1998, but took a sharp rise after the attacks on Sept. 11, 2001, which killed nearly 3,000 people.

The Obama administration began making military budget cuts during efforts to end U.S. military operations in Iraq and Afghanistan, but now military spending is on the rise again - thanks to Russia and China.

Speaking exclusively with VOA, the Assistant Secretary of State for Political-Military Affairs R. Clarke Cooper called Russia and China "revisionist powers that would like to be in a place where they're not."

"I wouldn't call this an arms race," Cooper said, "but what is different is that we are in places that are more competitive than they were in the past."

The United States accounts for more than a third of global military spending.

It boasts 11 aircraft carriers, a powerful nuclear arsenal, new elite fighter jets and about 2.1 million troops. Experts agree its military remains the dominant force.

"I think sometimes there's a tendency to make Russia and China 30 feet tall, and they're not," Bradley Bowman, a former military officer and a current senior director at the Foundation for Defense of Democracies, told VOA. "There are real vulnerabilities there that we could exploit in a conflict, but there are also areas where they're more advanced than we are."

'Coerce and defeat'

China is now the world's second-largest military spender - going from just 2% of the world's military budget in 1990 to 14% now.

Bowman warned allies and partners that China has undertaken this comprehensive effort to modernize its military in order to "coerce and defeat" the U.S. and its allies in a future conflict.

China built two aircraft carriers in the past decade, and a third is under construction. China has developed its own elite fighter jets, troop numbers have swelled to more than 2.5 million, and it is investing in new technologies, including hypersonics weapons that would fly five times the speed of sound.

Wezeman says the swift modernization has been "perceived as a threat by its neighbors."

Other top spenders

In reaction, India has upped its military spending by more than $11 billion in just three years, now ranking fourth overall behind Saudi Arabia.

Although Russia slipped from the top five spending countries in 2018, it still has NATO's attention after invading Georgia in 2008 and annexing part of Ukraine in 2014.

The 29 NATO countries spent $963 billion, 53% of world military spending, in 2018.

That number is likely to increase as the U.S. continues to pressure NATO allies to spend 2% of their Gross Domestic Product on defense.

"We can't let countries off the hook," U.S. Defense Secretary Mark Esper said Saturday at the Royal United Services Institute in London. "You can't simply substitute and say, 'Well, my 2% is going to go to technology, or I'm going to build infrastructure. I can't deter a Russian brigade with a road.' We need real capability."